a. Field of the Invention
This invention relates to a control system for an in-cylinder direct injection engine which controls the behavior of fuel spray, directly injected into a combustion chamber in a cylinder, with a tumble to combust a mixture stratified around an electrode of a spark plug, and more particularly relates to the technical field of compensation control for compensating an influence on combustion quality of the mixture resulting from intake air density conditions different than desired.
b. Description of the Prior Art
Conventionally, control systems for in-cylinder direct injection engines of this type include one which is adapted to control the penetration of fuel spray from an injector in accordance with the intensity of a tumble, carry the fuel spray toward a spark plug by means of the tumble and stratify a mixture around an electrode of the spark plug, as disclosed in, for example, Japanese Unexamined Patent publication No. 2000-204954.
Specifically, in the above control system, a tumble control valve (TCV) is provided in an intake passage of the engine downstream of a throttle valve. The TCV is opened or closed by an actuator to control the intensity of the tumble in the combustion chamber. At the same time, the fuel injection pressure of the injector is correspondingly controlled so that the fuel spray penetration is balanced against the tumble. In this manner, the fuel spray from the injector is carried by means of the tumble to reach the vicinity of the electrode of the spark plug, which enables stable stratified combustion.
More specifically, the fuel injection pressure of the injector is experimentally set in advance to change depending upon operating conditions of the engine, and stored as a control map. A value corresponding to the current operating conditions of the engine is read out as a target value for control from the map. Then, the fuel injection pressure of the injector (fuel pressure) is controlled to match the target value so that the fuel spray penetration is balanced against the tumble intensity. The fuel spray is thereby carried by means of the tumble to reach the vicinity of the electrode of the spark plug at the exact ignition timing of the cylinder.
In general, since the temperature of the engine is relatively high as compared with that in the air, the temperature conditions of an intake air taken in the combustion chamber is strongly affected by the engine temperature conditions. In addition, a change in temperature of the intake air involves a change in density thereof, which varies the energy of tumble in the combustion chamber. Therefore, even if attempt is made to control the fuel injection pressure of the injector in accordance with the preset map as in the above-mentioned prior art, the fuel spray and the tumble may be thrown out of balance depending upon the engine temperature conditions so that a mixture may be held against stratification, which invites inconveniences of deterioration in ignitability and combustion quality of the mixture.
Particularly in an engine that performs so-called EGR (Exhaust Gas Recirculation) by recirculating part of an exhaust gas to an intake system, the recirculation rate of exhaust gas to fresh air is generally changed in accordance with the engine operating conditions. This change in recirculation rate of high-temperature exhaust gas causes a significant variation in temperature conditions of the intake air. Accordingly, in the engine of this type, the above inconveniences are more pronounced.
Further, for example, in relatively low atmospheric pressure environments such as highlands, the air density is relatively low as compared with flatlands so that the energy of tumble becomes smaller than that in flatlands. Also in this case, like the above-mentioned prior art, a mixture is held against stratification if the fuel injection pressure of the injector is controlled only in accordance with a preset control map.
The present invention has been made in view of the foregoing points, is directed to a control system for an in-cylinder direct injection engine which controls the behavior of fuel spray with a tumble to provide suitable mixture stratification, and has its object of preventing the fuel spray and the tumble from being thrown out of balance due to a change in intake air temperature or atmospheric pressure and of providing suitable mixture stratification.
To attain the above object, in the present invention, when an engine is in operation, a value for density conditions of an intake air taken in a combustion chamber is detected, and at least one of the flow rate of ah tumble in the combustion chamber, the fuel injection pressure and the fuel injection timing is compensated so that the intensity of the tumble and the penetration of fuel spray are balanced one against another.
Specifically, a first aspect of the invention has as a precondition a control system (A) for an in-cylinder direct injection engine which includes: a fuel injection valve (18) for directly injecting a fuel into a combustion chamber (6) in a cylinder (2) of an engine (1); and tumble generating means (10) for generating a tumble in the combustion chamber (6), in which the fuel is injected against the tumble in the combustion chamber (6) by the fuel injection valve (18) during stratified-charge combustion operation of the engine (1) so that a flammable mixture stays in the vicinity of an electrode of a spark plug (16) at the ignition timing for the cylinder (2).
Also, the control system (A) further includes: intake air density detecting means (50a) for detecting a value for density conditions of an intake air taken in the combustion chamber (6); revolving speed detecting means (52) for detecting the revolving speed of the engine (1); intake air flow control means (34) for controlling the flow rate of the tumble in the combustion chamber (6); fuel pressure control means (20) for controlling the fuel injection pressure of the fuel injection valve (18); and control means (50) for controlling the fuel injection valve (18), the intake air flow control means (34) and the fuel pressure control means (20) based on a value detected by at least one of the intake air density detecting means (50a) and the revolving speed detecting means (52), wherein the control means (50) sets based on at least the engine revolving speed respective reference target values of the tumble flow rate, fuel injection pressure and fuel injection timing that correspond to the case where the value for density conditions of the intake air is equal to a preset reference value, and the control means (50) compensatorily modifies at least one of the reference target values based on a value for the difference between the value detected by the intake air density detecting means (50a) and the reference value.
First, according to part of the control system (A) which constitutes the precondition, the fuel is injected from the fuel injection valve (18) against a tumble generated by the tumble generating means (10) during stratified-charge combustion operation of the engine (1). In this case, the flow rate of the tumble, the fuel injection pressure and the fuel injection timing are basically controlled by the control means (50) based on at least the engine revolving speed. Therefore, if the intake air density is equal to the reference value, the penetration of fuel spray from the fuel injector (18) is balanced against the tumble so that a mixture is stratified around the electrode of the spark plug (16) at the exact ignition timing of the cylinder (2).
However, for example, if the engine (1) is in higher temperature conditions than normally it is, the intake air will be relatively high in temperature and thereby low in density. In such a case, the energy of tumble becomes relatively small so that the tumble and the fuel spray are thrown out of balance. This inhibits suitable stratification of the mixture and thereby impairs the ignitability and combustion quality thereof.
On the other hand, according to the above-mentioned characteristic structure of the invention, the value for density conditions of the intake air taken in the combustion chamber (6) of the cylinder (2) of the engine (1) is detected by the intake air density detecting means (50a), and at least one of the target values for controlling the tumble flow rate, the fuel injection pressure and the fuel injection timing, respectively, is compensatorily modified by the control means (50) to reduce the influence of an energy drop of the tumble, based on a value for the difference between the detected value and the reference value, i.e., if the detected value is a value indicating a lower density than the reference value (second aspect of the invention). Accordingly, a mixture can be suitably stratified as initially intended. This provides enhanced ignitability and combustion quality of the mixture and thereby provides well improved fuel economy and power output performance.
In a third aspect of the invention, the intake air density detecting means (50a) detects at least one of the intake air temperature, the atmospheric pressure and the rate at which an exhaust gas is recirculated to an intake system.
In this manner, a change in intake air density can precisely be detected based on the detected value of the intake air temperature or the atmospheric pressure. Alternatively, if the recirculation rate of exhaust gas is detected, a change in intake air temperature due to recirculation of high-temperature exhaust gas can be obtained based on the detected value. A change in intake air density can be accordingly detected.
In a fourth aspect of the invention, an intake air passage (30) of the engine (1) is connected with an end of an exhaust gas recirculation passage (43) for recirculating part of the exhaust gas from an exhaust system to an intake system, and the intake air density detecting means (50a) is configured to detect temperature conditions of the intake air downstream from a connecting point with the exhaust gas recirculation passage (43).
In this manner, the temperature conditions of the intake air, including influences due to recirculation of high-temperature exhaust gas to the intake air passage (30), can precisely be detected. Based on this detection result, a change in intake air density and further an out-of-balance relation between the tumble and the fuel spray can be detected.
In a fifth aspect of the invention, the control system (A) further includes: reference intake air density storage means in which reference values for density conditions of the intake air are stored in correspondence with different operating conditions of the engine (1); comparison means for comparing the reference value stored in the reference intake air density storage means with the value detected by the intake air density detecting means (50a); and compensation amount setting means (50d) for setting an amount of compensation for at least one of the tumble flow rate, the fuel injection pressure and the fuel injection timing based on the comparison result of the comparison means (50d).
With this arrangement, the reference values for intake air density conditions are first preset so as to correspond to respective operating conditions of the engine (1), and then stored in the reference intake air density storage means. When the engine (1) is in operation, the reference value corresponding to its current operating conditions is compared with the detected value of the intake density detecting means (50a) by the comparison means (50b), and based on the comparison result, the compensation amount setting means (50d) sets an amount of compensation for at least one of the target values of tumble flow rate, fuel injection pressure and fuel injection timing. In this manner, the amount of compensation at which the control means (50) should compensate can be set in accordance with the degree of unbalance between the tumble and the fuel spray, and suitable compensation control can be made to eliminate such unbalance in just proportions.
In a sixth aspect of the invention, the control means (50) is configured to compensatorily modify the target value of the tumble flow rate to a larger value than the reference target value thereof when the detected value of the intake density detecting means (50a) indicates a lower density than the reference value.
In this manner, even if the energy of tumble is reduced due to a drop in intake air density, the influence due to this energy drop can be alleviated by increasing the tumble flow rate. This provides suitable mixture stratification as initially intended thereby fully attaining the operations and effects of the first aspect of the invention.
In a seventh aspect of the invention, the control means (50) is configured to compensatorily modify the target value of the fuel injection pressure to a smaller value than the reference target value thereof when the detected value of the intake density detecting means (50a) indicates a lower density than the reference value.
In this manner, even if the energy of tumble is reduced due to a drop in intake air density, the energy of fuel spray traveling against the tumble is reduced so that they can be balanced one against another. This provides suitable mixture stratification as initially intended thereby fully attaining the operations and effects of the first aspect of the invention.
In an eighth aspect of the invention, the control system further includes fuel pressure detecting means (19a) for detecting the fuel injection pressure of the fuel injector (18), and wherein the control means (50) is configured to compensate the fuel injection timing of the fuel injector (18) to the retard side until the deviation between the modified target value of the fuel injection pressure and the detected value of the fuel pressure detecting means (19a) has reached a predetermined value or less.
In general, control on the fuel injection pressure involves delay in response. Therefore, until the fuel pressure has reached the target value, the tumble and fuel spray may be transiently thrown out of balance to deteriorate the ignitability and combustion quality of the mixture. In contrast, in this aspect of the invention, the fuel injection timing is compensated during such a delay in control on the fuel pressure so that the transient deterioration in mixture ignitability and combustion quality can be blocked. Specifically, when the intake air density is low and the energy of tumble is dropped, i.e., when the penetration of fuel spray is intense relative to the tumble, the injection timing is retarded to provide suitable mixture stratification.
In a ninth aspect of the invention, the control means (50) is configured to compensatorily modify the target value of the fuel injection timing to the retard side with respect to the reference target value when the detected value of the intake density detecting means (50a) indicates a lower density than the reference value.
In this case, if the energy of tumble is dropped due to a decrease in intake air density, the injection timing of a fuel to be injected against the tumble is retarded. Thus, even if the fuel spray has a relatively intense penetration, a mixture can be formed in the vicinity of the spark plug (16) electrode at a desired timing. This fully attains the operations and effects of the first aspect of the invention.
In a tenth aspect of the invention, when the detected value of the intake air density detecting means (50a) indicates a higher density than the reference value, the control means (50) compensatorily modifies at least one of the target values for the tumble flow rate, the fuel injection pressure and the fuel injection timing to reduce the influence of an energy rise of the tumble.
With this arrangement, the value for density conditions of an intake air taken in the combustion chamber (6) of the cylinder (2) of the engine (1) is detected by the intake air density detecting means (50a). When the detected value indicates a higher density than the reference value, at least one of the target values for control on the tumble flow rate, fuel injection pressure and fuel injection timing is compensatorily modified by the control means to reduce the influence of an energy rise of the tumble.
In this manner, even if the intake air density is higher than the reference value, a mixture can be suitably stratified as initially intended, which enhances the ignitability and combustion quality of the mixture and thereby provides fully improved fuel economy and power output performance.
In an eleventh aspect of the invention, the control means (50) in the tenth aspect is configured to compensatorily modify the target value of the tumble flow rate to a smaller value than the reference target value thereof when the detected value of the intake air density detecting means (50a) indicates a higher density than the reference value.
In this manner, even if the energy of tumble is raised due to an increase in intake air density, the influence of this energy rise can be alleviated by reducing the tumble flow rate. This provides suitable mixture stratification as initially intended thereby fully attaining the operations and effects of the tenth aspect of the invention.
In a twelfth aspect of the invention, the control means (50) in the tenth aspect is configured to compensatorily modify the target value of the fuel injection pressure to a larger value than the reference target value thereof when the detected value of the intake density detecting means (50a) indicates a higher density than the reference value.
In this manner, even if the energy of tumble is raised due to an increase in intake air density, the energy of fuel spray traveling against the tumble is increased so that they can be balanced one against another. This provides suitable mixture stratification as initially intended thereby fully attaining the operations and effects of the tenth aspect of the invention.
In a thirteenth aspect of the invention, the control system further includes fuel pressure detecting means (19a) for detecting the fuel injection pressure of the fuel injector (18), and wherein the control means (50) is configured to compensate the fuel injection timing of the fuel injector (18) to the advance side until the deviation between the modified target value of the fuel injection pressure and the detected value of the fuel pressure detecting means (19a) has reached a predetermined value or less.
Thus, until the fuel pressure has reached the target value because of delay in response to the control on the fuel pressure, the fuel injection timing is compensated so that the transient deterioration in mixture ignitability and combustion quality can be blocked.
In a fourteenth aspect of the invention, the control means (50) in the tenth aspect is configured to compensatorily modify the target value of the fuel injection timing to the advance side with respect to the reference target value when the detected value of the intake density detecting means (50a) indicates a higher density than the reference value.
In this case, if the energy of tumble is raised due to an increase in intake air density, the injection timing of a fuel to be injected against the tumble is advanced. Thus, even if the fuel spray has a relatively weak penetration, a mixture can be formed in the vicinity of the spark plug (16) electrode at a desired timing. This fully attains the operations and effects of the tenth aspect of the invention.
In a fifteenth aspect of the invention, an in-cylinder direct injection engine system includes: an intake port (10) capable of generating a tumble in a combustion chamber (6) of an engine (1); a fuel injection valve (18) for injecting a fuel against the tumble in the combustion chamber (6) during a compression stroke of the cylinder (2); an intake air temperature sensor (46) for detecting the temperature of an intake air taken in the combustion chamber (6); an atmospheric pressure sensor (47) for detecting the atmospheric pressure; a revolving speed sensor (52) for detecting the revolving speed of the engine; an intake air flow control valve (34) for controlling the flow rate of the tumble flowing in the combustion chamber (6); a regulator (27) for regulating the fuel pressure of the fuel to be supplied to the fuel injection valve (18); and a control unit (50) for controlling the opening of the intake air flow control valve (34), and the fuel injection timing and fuel pressure of the fuel injection valve (18) based on a signal output from at least one of the revolving speed sensor (52), the intake air temperature sensor (46) and the atmospheric pressure sensor (47).
Further, the control unit (50) sets based on at least the engine revolving speed respective reference target values of the tumble flow rate, fuel injection pressure and fuel injection timing that correspond to the case where a value for density conditions of the intake air is equal to a preset reference value, calculates the intake air density based on the detected values of the intake air temperature sensor (46) and the atmospheric pressure sensor (47), and compensatorily modifies at least one of the reference target values based on a value for the difference between the calculated value for the intake air density and the reference value.
Further, it is preferable that when the calculated value for the intake air density indicates a lower density than the reference value, the control unit (50) having the above structure compensatorily modifies at least one of the target values for the tumble flow rate, the fuel injection pressure and the fuel injection timing to reduce the influence of an energy drop of the tumble, and that when the calculated value for the intake air density indicates a higher density than the reference value, the control unit (50) compensatorily modifies at least one of the target values for the tumble flow rate, the fuel injection pressure and the fuel injection timing to reduce the influence of an energy rise of the tumble (sixteenth aspect of the invention)
With this structure, the same operations and effects as in the first aspect are exhibited.
As described so far, according to the first aspect of the invention, in the control system for an in-cylinder direct injection engine in which a tumble is generated to flow toward an injector in a combustion chamber of a cylinder during stratified-charge combustion operation of the engine and a fuel is injected against the tumble with a suitable penetration so that a flammable mixture which stays in the vicinity of the spark plug electrode is ignited at the exact ignition timing of the cylinder, a value for density conditions of the intake air taken in the combustion chamber in each cylinder is detected, and at least one of the tumble flow rate, the fuel injection pressure and the fuel injection timing is compensated based on the detected value so that the tumble intensity and the fuel spray penetration are substantially balanced one against another in the combustion chamber. Therefore, for example, even if the intake air temperature or the atmospheric pressure is changed and the energy of tumble thereby varies, the tumble and the fuel spray can be prevented from being thrown out of balance so that a mixture can be suitably stratified as initially intended. This enhances the ignitability and combustion quality of the mixture thereby providing well improved fuel economy and power output performance.
According to the second aspect of the invention, when the energy of tumble is dropped due to change in intake air temperature, atmospheric pressure and so on, the effects as in the first aspect can be fully obtained.
According to the third aspect of the invention, since the intake air density detecting means detects at least one of the intake air temperature, the atmospheric pressure and the recirculation rate of exhaust gas, a change in intake air density can precisely be detected based on the detected value in order to perform compensation control. It can be thereby prevented that the tumble and the fuel spray are thrown out of balance due to change in density conditions of the intake air.
According to the fourth aspect of the invention, since the intake air density detecting means detects temperature conditions of the intake air downstream from a connecting point with the exhaust gas recirculation passage, the temperature conditions of the intake air, including influences due to recirculation of high-temperature exhaust gas, can precisely be detected. Through compensation control based on this detection result, the tumble and the fuel spray can be prevented from being thrown out of balance.
According to the fifth aspect of the present invention, the detected value for density conditions of the intake air is compared with the reference value corresponding to the current engine operating conditions, and based on this comparison result, the amount of compensation of the control means is set. Therefore, in accordance with the degree of unbalance between the tumble and the fuel spray, suitable compensation control can be made to eliminate such unbalance in just proportions.
According to the sixth aspect of the invention, even if the energy of tumble is reduced due to a drop in intake air density, the influence due to this energy drop can be alleviated by increasing the tumble flow rate. This provides suitable mixture stratification as initially intended.
According to the seventh aspect of the invention, even if the energy of tumble is reduced due to a drop in intake air density, the energy of fuel spray traveling against the tumble is reduced so that they can be balanced one against another. This provides suitable mixture stratification as initially intended.
According to the eighth aspect of the invention, since the fuel injection timing is compensated to the retard side until the actual fuel injection pressure has reached the modified target value by compensation control on the fuel pressure, the influence of an energy drop of the tumble can be alleviated. Therefore, even if the delay in control over the fuel pressure is relatively large, a mixture can suitably be stratified to prevent transient deterioration in combustion quality and the like.
According to the ninth aspect of the invention, even if the energy of tumble is dropped due to a decrease in intake air density, the injection timing of a fuel to be injected against the tumble is retarded. This enables fuel spray to reach the vicinity of the spark plug electrode at a desired timing, thereby providing suitable mixture stratification as initially intended.
According to the tenth aspect of the invention, when the energy of tumble is raised due to a change in intake air temperature or atmospheric pressure, the effects as in the first aspect of the invention can fully be obtained like the second aspect of the invention.
According to the eleventh aspect of the invention, even if the energy of tumble is raised due to an increase in intake air density, the influence of this energy rise can be alleviated by reducing the tumble flow rate. This provides suitable mixture stratification as initially intended.
According to the twelfth aspect of the invention, even if the energy of tumble is raised due to an increase in intake air density, the energy of fuel spray traveling against the tumble is increased so that they can be balanced one against another. This provides suitable mixture stratification as initially intended.
According to the thirteenth aspect of the invention, since the fuel injection timing is compensated to the advance side until the actual fuel injection pressure has reached the modified target value by compensation control on the fuel pressure, the influence due to an energy rise of the tumble can be alleviated. Therefore, even if the delay in control over the fuel pressure is relatively large, the mixture can suitable be stratified to thereby prevent transient deterioration in combustion quality and the like.
According to the fourteenth aspect of the invention, even if the energy of tumble is raised due to an increase in intake air density, the injection timing of a fuel to be injected against the tumble is advanced. This enables fuel spray to reach the vicinity of the spark plug electrode at a desired timing thereby providing suitable mixture stratification.
According to the in-cylinder direct injection engine system of the fifteenth and/or sixteenth aspect of the invention, the same effects as in the first aspect can be obtained.